1. Field of the Invention
The present general inventive concept relates to a sound reproduction apparatus and method, and more particularly, to a sound reproduction apparatus and method capable of enhancing a low frequency component in a reproduced sound signal using a reflective sound.
2. Description of the Related Art
A small speaker adopted in headphones, earphones, or portable audio devices is restricted in producing a low sound. To overcome this restriction, a sound signal is conventionally reproduced by enhancing or amplifying a signal corresponding to a low frequency component. However, when the signal corresponding to the low frequency component is increased, a level of a low frequency signal is also increased, for example, due to an overflow of the low frequency signal in an equalizer. To prevent the overflow of the low frequency signal, a dynamic range of an input signal must be considerably reduced, which may deteriorate quality of a finally reproduced sound.
U.S. Pat. No. 6,285,767B1 discloses a “low frequency audio enhancement system” that can enhance a low frequency component.
FIG. 1 is a block diagram illustrating a conventional low frequency enhancement system. Referring to FIG. 1, the low frequency enhancement system comprises a composite filter 1707 employing a band pass filter, a peak compressor 2502 that compresses an output peak value of the composite filter 1707, and a punch unit 1720. The conventional low frequency audio enhancement system uses a mental acoustic approach method (psychoacoustic technique), for example, that a person listening to acoustic energy at 50 Hz and 60 Hz mentally perceives acoustic energy at 110 Hz or a person listening to acoustic energy at 100 Hz and 150 Hz mentally perceives acoustic energy at 50 Hz.
An adder 1706 adds two input signals 1702 and 1733. The composite filter 1707 extracts low frequency components from the added signal using filters 1711, 1715, 1712, 1713, and 1714 having frequency bands 50, 250, 100, 150, and 220 Hz, respectively, adds the extracted low frequency components, and outputs the added low frequency components through a switch 1722 and an adder 1718. The peak compressor 2502 prevents an overflow caused by the addition of the extracted low frequency components. In detail, as a plurality of low frequency band pass filters output low frequency component signals, a sum of the low frequency component signals has an increased peak value, which may cause the overflow. If an output signal only is standardized to reduce the peak value, a low frequency enhancement effect is removed. Therefore, even if a non-linearly low level signal increases its level, the increased level remains in a dynamic range of the conventional low frequency enhancement system, thereby maintaining the low frequency enhancement effect. The punch unit 1720 expands a release time of a low frequency component to allow a listener to listen to the low frequency component for more prolonged time, thereby increasing the low frequency enhancement effect. An output of the punch unit 1720 is added to the input signals at adders 1724 and 1732 through a switch 1722 to generate output signals 1730 and 1733.
However, the conventional low frequency audio enhancement system has a complex constitution since an amount of calculation increases due to a large number of low frequency band pass filters, and an additional device, such as the peak compressor 2502 is required to adjust the dynamic range of the conventional low frequency enhancement system. Also, when the punch unit 1720 only enhances the low frequency component, a listener has no externalization when listening to sounds through headphones, etc.
Japanese Patent Publication Application No. Hei 5-328481 discloses a frequency doubling and mixing circuit that enhances a low frequency component by forming a harmonic component of an input signal. The frequency doubling and mixing circuit includes a radio rectifier and a low band filter to generate a low pass filter and the harmonic component. The frequency doubling and mixing circuit obtains a frequency component that requires the formation of the harmonic component using the low pass filter from the input signal, generates the harmonic component that doubles a frequency component using the radio rectifier from the obtained signal at a frequency position higher by one octave, and enhances a mental acoustic of the low frequency component. However, the frequency doubling and mixing circuit uses the radio rectifier to forcibly clip or invert the input signal in order to generate the harmonic component, which may greatly deteriorate the sound quality.
As described above, although these conventional sound reproduction methods enhance a low frequency component such that a user perceives an illusionary low frequency component in terms of mental acoustic to generate a harmonic component, such that the sound quality is deteriorated by clipping an input signal, or the constitution that is complex due to various filtering and additional apparatuses. Also, the low frequency component enhanced by these conventional sound reproduction methods is generally a mono component. Therefore, when a listener listens to a signal having the mono component through headphones, earphones, etc., a higher energy low frequency component is centered in a brain, what is called, brain localization, which causes coercion or fatigue.